Double hermetic seal for gaseous discharge lamps



Aug. 30, 1955 T. c. RETZER DOUBLE HERMETIC SEAL FOR GASEOUS DISCHARGE LAMPS 3 Sheets-Sheet 1 Filed Dec.

INVENTOR.

Aug. 30, 1955 T. c. RETZER 2,716,584

DOUBLE HERMETIC SEAL FOR GASEOUS DISCHARGE LAMPS Filed D80. 16, 1953 3 Sheets-Sheet 3 S: W10 y/ I "P I INVENTOR. 7': 6'. 357267? QAQ United States Patent DOUBLE HERMETIC SEAL FOR GASEOUS DISCHARGE LAMPS Theodore C. Retzer, Cedar Grove, N. 1., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 16, 1953, Serial No. 398,500 1 Claim. (Cl. 31619) The present invention relates to seals and, more particularly, to a double hermetic seal for high temperature, high pressure gaseous discharge lamps and the method of manufacture thereof.

In the manufacture of high temperature, high pressure gaseous discharge lamps the main problem encountered is the prevention (during operation of the lamp) of the loss of gas fill or mercury vapor from the quartz envelope body through the hermetic seal in the end tube affixed thereto. It is hence essential that this hermetic seal between the rod-like leading-in conductor and the end tubes be made as close to the are tube body as possible. In the past, ribbon seals and disc seals of various types have been employed without satisfactorily accomplishing the solution to the problem.

One of the more recent attempts to achieve a satisfactory disc seal is exemplified by U. S. Patent No. 2,630,471 entitled Quartz-to-Metal Seal, issued to Leo R. Peters and assigned to the General Electric Company. A cup shaped thin molybdenum disc having a feathered peripheral edge is brazed to a refractory leading-in conductor or rod suitably spirally wrapped with a thin molybdenum foil. The disc is surrounded on both sides successively by molybdenum foil washers and then by an overlapping vitreous annular wafer suitably of smaller thickness than the molybdenum disc. Seals of this type all require complicated processing set-ups, are difiicult to manufacture with semi-skilled and semi-automatic equipment and often produce fractures between the disc and the end tube wall, thus permitting the above mentioned gas or mercury vapor escape. In addition, this seal permits the oxidation (during operation) of the spiral molybdenum wrapping on the leading-in conductor and the molybdenum disc thus leading to eventual deterioration of the hermetic seal.

Hence, it has been found advantageous according to my invention to employ a double hermetic seal between the refractory leading-in conductor or rod and the quartz end tube to prevent escape of the mercury vapor or the gas fill from the envelope body into the end tubes thereof due to fracture of the seal. Further my double hermetic seal eliminates possible oxidation of the molybdenum wrapping and disc. The seal of my invention comprises a simplified disc seal between the leading-in rod and the end tube near the envelope body and a second hermetic graded buffering or protective seal between the end tube and the outer portions of the leading-in rod.

In its general aspect the present invention has as its objective a double hermetic seal for a high pressure, high temperature discharge device between a refractory leading-in conductor and a quartz end tube thereof.

A specific object of the present invention is a double hermetic seal for a gaseous discharge device comprising a disc seal for a gaseous discharge device between a refractory leading-in conductor rod and an end tube close to the envelope body thereof and a lower graded buffering seal between a graded portion of the end tube and the outer portion of the leading-in rod.

Patented Aug. 30, 1955 'ice Other objects of the present invention will become apparent to those skilled in the art to which it appertains as the description thereof proceeds.

Referring now to the drawings in which like numerals of reference indicate similar parts throughout the several views:

Fig. 1 is a side elevational view, partially in section, of a high temperature, high pressure gaseous discharge lamp wherein the double hermetic seal of my invention is contained.

Fig. 2 is an alternative embodiment of one of the double hermetic seals of my invention for the gaseous discharge lamp of Fig. 1 and showing a refractory leading-in conductor having a flexible internal portion to facilitate contraction and expansion thereof during the cooling and heating of the parts.

Fig. 3 is a side elevational view partially in section showing the assembly of a refractory disc and the upper and lower members of the leading-in rod or conductor of Fig. 1.

Fig. 4 is a view similar to Fig. 3 and showing the upper and lower members of the leading-in conductor spirally wrapped with a thin molybdenum ribbon and an upper vitreous washer in place about the conductor and resting on the disc.

Fig. 5 is a side sectional view of a thin molybdenum disc having a feathered peripheral edge and employed in the first hermetic seal close to the envelope body.

Fig. 6 is a perspective view of the relatively thick vitreous washers employed in the disc seal adjacent the envelope body.

Fig. 7 is a side elevational view partially in section and showing the sealing of a washer skirt extension tube to the lower portion of the end tube.

Fig. 8 is a View similar to Fig. 7 and showing the formation of the second or graded hermetic protective seal between the lower portions of the end tube and the leading-in conductor rod.

Fig. 9 is a view similar to Figs. 7 and 8 showing the exhausting of the sealed end tube and the final collapsing of the vitreous washers and the washer skirt extension tube about the disc and the wrapped portions of the leading-in conductor.

Fig. 10 is a view similar to Figs. 7, 8 and 9 showing the cutting-off of the upper portion of the now sealed end tube.

Fig. 11 is a side elevational view showing the sealing of the envelope body to the upper end of the now double hermetically sealed end tube.

Referring now to Fig. 1 the reference numeral 10 designates a high pressure, high temperature gaseous discharge lamp. This lamp It) has a vitreous envelope 12, for example quartz, which may suitably comprise a gener ally holiow spherical body 14 to which end tube electrode assemblies 15 (Fig. 10) are sealed. In turn each of the assemblies 15 comprises an end tube 16 to which an electrode assembly 13 is double hermetically sealed.

End tubes As shown particularly in Figs. 1, 2 and 7 each of the end tubes 16, suitably quartz or Vycor, may be fabricated in two parts, namely an upper tube assembly 19 and a lower tube assembly 24). Vycor is the trade name for a refractory glass having 96% silica. This upper assembly 19 may comprise an upper tube 21 having a washer skirt extension tube 22 of larger diameter sealed to, and about, its lower portion. This skirt tube 22 extends substantially beyond the lower portions of the upper tube 21. Each lower tube assembly 20 has a lower tube 24, suitably of the same diameter as the upper tube 21 having a Vycor grade or step 26 butt sealed to its lower end. A graded seal or tube 28, suitably multiform and having a plurality of steps, for example eight, has its relatively hard glass upper end sealed to the Vycor step 26, to complete the lower tube assembly 20.

Electrode assemblies Each of the electrode assemblies 18 has a refractory leading-in conductor or rod 30, suitably molybdenum or tungsten depending on the relatively soft glass end of the graded seal employed. As shown in Figs. 3 and 4 this rod 30 comprises an upper member 32 and a lower member 34. An axial lower rod-like projection 35 of the upper member 32 is suitably smaller in diameter than the upper member 32 and fits into an axial cavity 36 machined in the upper portion of the lower member 34. The mouth of the axial cavity 36 is conveniently larger in diameter than the projection 35 of the upper member 32 to permit the loading or insertion therein of appropriate brazing material 38, such as platinum or other suitable high temperature solders which melt at or about the softening temperatures of quartz. A thin molybdenum disc 40 having a feathered peripheral edge is carried between the upper member 32 and the lower member 34. The upper end of the upper member 32 carries an electrode 42.

The molybdenum disc 40, generally elliptical in cross section (as shown in Fig. 5) may have a minor axis, for example, ranging in thickness from .0010 to .0015" and its thin peripheral feathered edge etched, by suitable electrolytic means, to a thickness of approximately .0006". An axial hole 44 is provided therein to permit the insertion of the projection 35 of the upper member 32 therethrough.

As shown in Fig. 4 the upper member 32 and the lower member 34 are suitably wrapped (after the above described assembly operation with the disc 40 and brazing material 38) with a spiral wrapping of thin molybdenum ribbon 46, approximately .0006" in thickness, in the conventional manner. To prevent damage of the feathered edge of the disc 40 during wrapping I have found it preferable to wrap the upper member 32 and the lower member 34 before assembly thereof with the disc 40.

As shown in Figs. 1, 2, 7, 8 and 9 the lower portion of the lower member 34 of the leading-in conductor 30 carries a vitreous bead 48 of a glass having expansion characteristics which match the relatively softer end of the graded tube 23, and the leading in conductor 18.

It will be understood that a lower member 34 of the conductor rod 30 may be fabricated in three parts as shown in Fig. 2. An upper portion 70 of the lower member 34' having the axial cavity 36 may be joined to a flexible braided cable portion 72. In turn a lower portion 74 which carries the vitreous head 48 is connected to the bottom of the cable portion 72. By employing this flexible lower member 34' any strains which may be produced in the double hermetic seals due to expansion and contraction of the parts during lamp operation may be eliminated.

Prior to the making of the first or upper hermetic disc seal, vitreous washers 50 (shown in Fig. 6), suitably quartz or Vycor, are inserted over the wrapped conductor 30 and positioned on the disc 40. These vitreous washers 50 are suitably much thicker than the disc 38, for example, .060 to .100" in thickness. The washers 50 are about 2 mm. larger in diameter than the molybdenum disc 40 in order to completely cover the delicate feathered edge thereof, during the sealing operation.

Preliminary disc seal As shown in Fig. 7 the upper tube assembly 19 of the end tube 16 (comprising the upper tube 21 and the surrounding skirt tube 22) is positioned about the vitreous washers 50 (with the disc 40) of the electrode assembly 18 therebetween). The lower end of the upper tube 21 rests on the upper washer 50. In turn the lower tube assembly 20 of the end tube 16 is inserted over the lower portion of the rod 30 of the electrode assembly 18 into position against the bottom washer 50.

A protective atmosphere, for example, forming gas, is permitted to flow through the assembled end tube 16 and electrode assembly 18 to prevent oxidation of the molybdenum ribbon 46 on the upper member 32 and the lower member 34 of the leading-in conductor 30 and the molybdenum disc 40 between the vitreous washers 50. A high temperature fire 60 is then directed against the lower portion of the skirt tube 22 and the adjacent portion 24 of the lower tube assembly 20 to heat the parts to the softening temperature of quartz and to drive the bottom portion of the skirt tube 22 in against the lower tube 24 of the lower tube assembly 20 thus permitting the sealing of the lower end of the skirt tube 22 to the lower tube 24 as shown in Fig. 8.

Graded seal As shown in Fig. 8, the now partially sealed end tube 16 and electrode assembly 18 are subjected to a protective atmosphere, for example forming gas and second high temperature fire 62. This fire 62 is directed at the relatively soft end of the graded tube 28 of the lower end tube assembly 20, and the lead 48 on the lower portion of lower member 34 of conductor 30. This relatively softer lower portion of the graded tube 28 is heated along with the bead 48 to the softening temperature of the glasses so that the bottom edge of the graded tube 28 is driven inwardly toward the bead 48 and is hermetically sealed thereto. The graded seal is substantially away from the zone of the high temperatures and high pressures achieved during operation of the lamp 10.

Final disc seal The end tube electrode assembly 15 is then transferred to an exhaust position and is evacuated by any suitable means such as a pump (not shown). As shown in Fig. 9, the skirt tube 22 of the upper end tube assembly 19, the vitreous washers 50, the disc 40 and the molybdenum wrapped portions 32 and 34 of the conductor 30 are all subjected to a relatively wide high temperature fire 64 which heats the above mentioned parts to the softening temperature of quartz. As is well-known in the art, the atmospheric pressure on the outside of the end tube 16 causes the upper end tube 21 and lower end tube 24 to collapse inwardly onto the ribbon 46 on the upper member 32 and the lower member 34 of the conductor 30. Simultaneously the washers 50 hermetically enclose the thin peripheral edge of the molybdenum disc and the skirt tube 22 collapses upon the outer surface of the upper tube 21, the lower tube 24 and the washers to hermetically seal the disc 40 therebetween and prevent any possible loss of gaseous fill or mercury vapor from the envelope body 14 into the end tube 16.

As shown particularly in Fig. 10, the upper end of the upper tube 21 is trimmed by a cutting wheel 66 slightly below the top of the molybdenum ribbon 46 on the upper member 32 of the conductor 30. The now desirably double hermetically sealed end tube assembly 15 is then sealed as shown in Fig. 11 by means of a high temperature fire 68 to the body 14.

It will be understood that a similar end tube electrode assembly 15 may be sealed to the opposite side of the and the relatively hard end of the graded seal 28 are not sunk down into contact with the rod 30. The cavity 30 therebetween is under vacuum and protects the disc 40 and the wrapping 46 from oxidation during lamp operation.

Although a preferred embodiment of my invention has been disclosed, it will be understood that modifications may be made within the spirit and scope of the invention.

I claim:

The method of making a double hermetic seal between an end tube and an electrode assembly comprising assembling an upper and lower vitreous washer about a thin refractory feathered edge metal disc of said electrode assembly, assembling an upper end tube assembly about said washers, said disc and said electrode assembly and a lower end tube assembly about said electrode assembly and in engagement with said lower washer, sealing in a protective atmosphere the bottom portion of a skirt tube of said upper end tube assembly to said lower end tube assembly, hermetically sealing in a protective atmosphere the lower relatively soft glass end of a graded seal portion of said lower end tube assembly to a bead on said electrode assembly, exhausting said now hermetically sealed end tube electrode assembly, collapsing said skirt tube and said washers about said disc to form a hermetic seal thereat, and also collapsing said upper end tube assembly and a portion of said lower end tube assembly onto a refractory ribbon wrapped conductor of said electrode assembly.

References Cited in the file of this patent UNITED STATES PATENTS 

